Lightning arrester



Jan. 17, 1950 s. w. ZIMMERMAN LIGHTNING ARRESTER Filed Jan. 12, 1945 I///IIII VII Inventor:

n m rw m n WW. .m o M A YW s m 3 ty Sb Patented Jan. 17, 1950 2,495,154LIGHTNING amms'ran Stanley W. Zimmerman, Dalton, Mass., assignor toGeneral Electric Company, a corporation of New York Application January12, 1945, Serial No. 572,508

3 Claims.

My invention relates to lightning arresters suchas are used for theprotection of electric power transmission lines and associated apparatusfrom the efiects of excessive voltages due to lightning, switchingoperations or other causes. Specifically my invention is an improvementon the disclosure of United States Letters Patent 2,151,559, McEachron,granted March 21, 1939, and assigned to the same assignee as the presentapplication.

Lightning arresters of the type disclosed in the above mentionedMcEachron patent, often referred to as station-type lightning arresters,consist in general of a gap structure connected in series with a currentlimiting element. The current limiting element should have the propertyof decreasing and increasing its resistance as the discharge currentincreases and decreases to such a degree that the voltage across thearrester during discharge is held to safe values for connectedapparatus. The gap structure performs the function of a circuit breakerby interrupting the power follow current permitted to flow through thearrester by the current limiting element. The gap structure must also besuch as to become conducting at a sufliciently low impulse voltage tomaintain a proper margin between the gap breakdown voltage and theinsulation strength of the apparatus protected by the arrester.

It is an object of my invention to provide an improved lightningarrester so constructed and arranged as to have these desirable featuresto a high degree.

It is another object of my invention to provide a lightning arresterwhich will operate satisfactorily under much more severe impulseconditions than similar arresters used heretofore.

Still another object of my invention is to provide a lightning arresterwith greatly improved gap sealing ability,

Further objects and advantages of my invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize my invention will be pointed out with particularity in theclaims annexed to and forming a part of this specification.

For a better understanding of my invention, reference may be had to theaccompanying drawing in which Fig. 1 is a sectional view of a lightningarrester constructed in accordance with my invention; Fig. 2 is anenlarged view, partly in section, of a portion of the gap structure ofFig. 1; Fig. 3 is a perspective view of a portion of the lightningarrester shown in Figs. 1 and a 2 2 and Fig. 4 is another illustrating amodification of my invention.

Referring now to the drawing, I have illus trated a lightning arrestergenerally indicated at l in Fig. 1, which includes an outer casinghaving a cylindrical wall portion 2 formed of weatherproof insulatingmaterial such as porcelain. The cylinder 2 is closed at its upper end bya metal end-fitting or plate 3 secured to the casing by cement so as toform a tight, protective seal. A metal cap 4 is bolted to the endfittingor plate 3 and is provided with a line terminal 5. A metal supportingbase 6 having a ground terminal I is bolted to a metal ring 8 which iscemented to the lower end of the insulating cylinder 2. The openingthrough the ring 8 into the cylinder 2 is closed by a metal plate 9. Ametal plate In is supported by screws ll resting on the plate 9, thedistance of the plate to above the plate 9 being adjustable by means ofthese screws II.

A second cylinder l2, formed of porcelain or other insulating material,is arranged inside the cylinder 2, the two cylinders being coaxial. Thisinner cylinder I2 is closed and sealed at its upper end by a metal capl3 and at its lower end by a metal cap I l. The inner cylinder I2 isformed with an inner flange l5 forming a shoulder which supports aplurality of coaxial resistance units I6, I1, l8, I9, 20. 2i and 22. Theresistance units ii to 22 inclusive are preferably of the form shown inthe above mentioned McEachron patent, although this particular numberneed not necessarily be used. Each of the resistance units IE to 22inclusive is formed as a hollow ring or disk with plane upper and lowerfaces. Each of the plane faces of each resistance disk has a metalcoating to which is soldered a metal plate 23 with a central opening.Projections from the inner edges of the two plates 23 ofeach resistanceunit are bent toward each other, their adjacent ends being spaced toform a discharge gap 24 in the opening through the unit.

Another form of resistance unit 26 is supported in the insulatingcylinder l2 between the flange l5 and the lower end cap l4, two suchunits being shown in Fig. 1. Each resistance unit 26 is in th form of aring open at one side, the spaced ends 21 of the open ring carryingmetal projections extending into the space surrounded by the ring wherethey are spaced to form the electrodes of a discharge gap. As is clearlydisclosed in the above mentioned McEachron patent, one end o t owerresistance unit 28 is secured to a enlarged sectional view I tongue 28bent from a plate 29 clamped between the end cap l4 and the insulatingcylinder l2. One end of the upper resistance unit 26 is connected by astrap 30 to an annular metal member 3| resting on the flange i under theresistance unti l6. The other two ends of the two resistance units 26are connected together by a strap 32. The assembly of the resistanceunits It to 22 inclusive and the resistance units 26 with their commoncasing formed by the insulating cylinder I2 and its end caps I3 and I4constitutes a sealed gap unit.

The current limiting element of lightning arrester I comprises aplurality of resistance plates or disks 33 arranged in a stack betweenthe upper cap I3 of the gap unit and the top plate 3, a spring 34between the plate 3 and the upper resistance unit 33 being provided tohold the resistance units 33 and the gap unit in place. The pressure ofthe spring 34 on the resistance units 33 may be regulated by means ofthe ad- Justing screws II. The resistance disks 33 may be spaced fromeach other by thin metal plates or spacers which are considerablysmaller in diameter than the resistance disks 33 as is disclosed in theabove mentioned McEachron patent. Preferably, however, the planesurfaces of the disks are covered with a metal coating to provide goodconductive contact between adjacent disks as well as between the upperdisk 33 and spring 34 and between the lower disk 33 and cap l3.

The resistance material in the resistance units I 6 to 22 inclusive and33 must have a high inverse voltage-resistance characteristic. That is,if a voltage applied across a piece of this resistance material isincreased, then the resistance of the material will decrease verygreatly and the current flowin through the material will consequentlyincrease very greatly. It is also important that there be very little,it any, time lag between the change in the voltage and the correspondingchanges in resistance and current. A suitable resistant material forthis purpose is disclosed in United States Patent No. 1,822,742,McEachron, granted September 8, 1931, and assigned to the same assigneeas the present application. As disclosed in that pat-.- ent, theresistance material described therein may have different predeterminedcharacteris-'- tics. Thus; although the resistance units 16 to 22,inclusive, are shown as being of similar size and shape, they may havedifferent resistances under the same voltage conditions. As indicated inFig. l, the resistances of these resistance units decreases from theunit I8 to the unit 22, the unit I5 having the highest resistance andthe unit 22 having the lowest resistance. It is not necessary, however,that the resistances be all difierent but the units may be arrangedingroups, the resistances of the units in each group being of the samevalue but the resistances of the units in different groups havingdiiierent values. As shown in Fig. 1, the units I6 and I! have thehighest resistance, the units l8 and I! have resistances somewhat lowerthan that of the units [6 and I1, and the units 20, 2| and. 22 havestill lower resistances. The resistance of each unit 26 should behighwhich may be partly due to the characteristic of the material usedin the unit but also largely due to the considerably smaller crosssection and longer current path as compared to the units IE to 22. Thecombined resistance of the two units 25 under high impulse voltageconditions may even be comparable to the entire resistance of all theother resistance units.

The arrangement described thus far is not my invent on but is disclosedand claimed in McEachron Patent 2,151,559, mentioned above. In thedisclosure of this McEachron patent it was important that the dischargegaps 24 and also the gaps associated with the units 26 occurwith aslittle time delay as possible after the voltages across these gaps haverisen to the predetermined value at which the discharges should takeplace. In the McEachron Patent 2,151,559 the electrodes of the dischargegaps are arranged side by side so that a discharge across any gap willilluminate the adjacent gap or gaps. This illumination or electronradiation has the effect of ionizing the adjacent gap or gaps andreducing the time lag between the application of voltage and thedischarge. Thus after the first gap of units 26 breaks down theremaining gaps will break down in succession with substantially no timelag. In order that the discharge gaps 24 may break down in succesion,the discharge gap 24 of the resistance unit I6 is alittle shorter thanthat of the resistance unit [1. If, however, the lengths of the gaps aresuccessively increased, they will soon become so long that flash-overwill occur across the surfaces of gap shunting resistances 16, H, l8,etc. rather than across the gaps 24 as intended. Also the impulsebreakdown of the arrester becomes too high with long gap settings. Asthe size of a gap increases with a correspond ing increase in thevoltage applied to it, the efliciency of the gap from the point of viewof its ability to interrupt a discharge or flow of current across itdecreases. In order therefore that the discharge gap 24 of the resstance unit l8 may not be too long this gap may be made as short as thatof resistance unit l6 but the resistance of the resistance unit I6 issmaller than that of the resistance unit Ill. The volttage at any timeacross the discharge gap of the resistance unit [6 will thus be greaterthan that across the gap of the resistance unit It and the former gapwill thus break down first.

-In like manner the resistances of the resistance units I8 and i9 may beof the same value but the length of the discharge gap of the resistanceunit l9 may be slightly greater than that of the discharge gap of theresistance unit I8.

As has been pointed out in the preceding paragraph, the unsatisfactoryoperation of the lightning arrester will result if the gap length isincreased together with a corresponding increase in voltage. I havediscovered that a lightning arrester of the type described above can bemade to operate satisfactorily under much more severe impulse conditionsthan present lightning arrester constructions if the possibility of asingle arc across several of the gaps 24 is completely eliminated. Tothis end I interpose between the respective units I B to 22 disk-likebarriers or members 35. These disk-like barriers are preferablyconstructed of conducting material, such as copper, thereby topartitionofi the gap structure with equal potential surfaces and divideup the ionized space into separate compartments. With this arrangementgreatly increased gap sealing ability is provided by introducingdefinite potential drops along any ionized path which may be establishedthrough the gap, thereby breaking up any long, relatively stable areinto shorter, less stable arcs. The ionization resulting from a se} veredischarge through the gaps in the arrester may cause an arc to strikeacross several of the gaps 24, as for example, from one of theelectrodes in resistance unit It to one of the gap electrodes connectedto resistance unit l9, thus by-passing the gaps in resistance units l8,l1, l8, and it. As a result of this arc, the follow current interruptingability of the arrester is reduced because of the number of gaps inseries with the arc in this example are reduced from 9 to 6. Thisundesirable arc path may occur even though the discharge started acrossthe electrodes of each of the gaps that are connected in parallel withthe resistance units, IE to 22 inclusive, and 28 and 21. These seriesarcs might transfer to the undesirable path short circuiting several ofthe series gaps after the discharge was started due to the great amountof gaseous ionization resulting from carrying a severe discharge. Withbarriers 35 in place, the number of gaps in series with the arc andhence the current interrupting ability will not be reduced even thoughthe arc may transfer from the intended electrodes 24 to the surfaces ofthe conducting barriers 35 at each end of the resistance unit that isconnected in parallel with the gap.

Because of the volume differences and because of the different times andenergy associated with each of the arc segments there will tend to beestablished a gaseous flow within the arc which will serve to disturbthe stability of these short are segments and favor arc extinction whencurrent flow is diminished, as when current direction reverses at twotimes during the period of one cycle on an alternating current circuit.

Although the disks'35 will greatly increase the current interruptingability of the lightning arrester and therefore enable it to operatesatisfactorily under much more severe impulse conditions, these diskswithout more will increase the spark potential of the arrester veryappreciably if they are opaque to electron radiations since they willinterfere with one gap illuminating the other. To overcome thisdifficulty each of the disks is provided with a plurality of openings36. Actually a single opening in each disk, if these openings were allin alignment so that radiation from one gap might affect the next gap,would be satisfactory. It is quite possible, however, that the disks 35may be shifted slightly so that a single opening in each disk might notbe in alignment with arcs between the electrodes of the gap above andthe gap below the disk 35. Therefore, to guard against stopping theintergap illuminating path a multiplicity of holes 35 are providedarranged somewhat in the manner of the holes in a salt shaker top,thereby allowing illumination without requiring any particular hole tobe in alignment with other holes or openings. The size of the holes indisks or barriers 35 is not importantinsofar as they do not become sosmall as to be mechanically diillcult to produce or so large that theydo not serve as proper shields or conducting surfaces if constructed ofmetal. I have discovered that holes as large as one-quarter inch indiameter are unsatisfactory, while holes as small as forty thousandthsof an inch were found very satisfactory.

Although I have found it preferable to employ disks 35 formed ofconducting material, satisfactory operation can be obtained withbarriers or disks formed of insulating material, such as fiber. Ifinsulating barriers are used, provisi'on must be made for conductingcurrent from gap to gap. Fig. 4 illustrates such an arrangement whereina barrier or disk 31 is employed which is similar to disk I! except thatit is made of insulating material and a plurality of spaced rivets ll ofconducting material are provided therein to conduct current from gap togap or between adjacent electrode plates 23. It will be obvious that ifthe barrier 31 is made of a material transparent to the activeradiations which aid in setting of! the successive gaps, the openings orholes 36 may be dispensed with. For example, if the barriers were madeof quartz, which is not a barrier to the ultra violet illumination whichis the effective illumination to aiding the gap breakglowln, openings 38might be dispensed with enre y. 1

In view of the detailed description included in McEachron Patent2,151,559, the operation of the lightning arrester embodying myinvention will be obvious particularly in the light of the detaileddiscussion included above. with the inter-gap barriers Bl the effect ofionized air allowing the'arc to communicate between electrodes ofadjacent gaps is completely eliminated. I have discovered that on testsmade at impulse currents of the order of 10,000 amperes, a markedincrease in satisfactory follow current interruptions occurred whenemploying the inter-gap barriers of my invention whereas unsatisfactoryoperation resulted with lightning arresters constructed in accordancewith the prior art.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects and I, therefore, aim in the appendedclaims to cover all such changes and modifications as fall within thetrue spirit and scope of my invention.

what I claim as new and desire to secure by Letters Patent ofthe UnitedStates is:

1. A lightning arrester including a pair of coaxially arranged hollowrings of resistance material, a metal plate with a central openingsecured to each face of each ring and having a projection from the inneredge of said opening, the ends of the projections associated with eachring forming a pair of spaced electrodes within the hollow of each ringand defining an arc gap therein, and a plurality of disk-like elementsof metal respectively interposed between and in physical contact withsaid metal plates positioned between each pair of adjacent rings toprevent an arc from extending between electrodes of different gaps. each01' said disk-like elements having a plurality of staggered openingstherein for permitting an arc at one of said gaps to illuminate theother gaps through one or more of said openings in said disk-likeelements even though said disk-like members are not in alignment.

2. A gap structure comprising a plurality of series are gaps, each gapbeing positioned between a pair of coaxially arranged spaced metalplates each of which has a central opening and a projection from theedge thereof, the ends of the projections associated with each of saidpair of plates forming a pair of spaced electrodes between the pair ofplates and defining an arc gap therein, and a barrier of conductingmaterial interposed between and in physical contact with the adjacentplates of each two adjacent pairs of plates for preventing an are fromstriking between an electrode of the gap within one of said adjacentpairs of plates and an electrode of another gap in said structure, saidbarrier having an opening therein through which radiation eflective toirradiate other gaps may pass.

3. A gap structure comprising a plurality of series are gaps, each gapbeing positioned between a pair of coaxially arranged spaced metalplates each of which has a central opening and a projection from theedge thereof, the ends 01 the projections associated with each 01 saidpair of plates forming a pair of spaced electrodes between the pair ofplates and defining an arc gap therein, and means for establishingelectrical connection between a plate 01' one of said pair of plates andthe adjacent plate of an adjacent pair .of plates including a barrierinterposed between and in physical contact with the adjacent 1 8structure, said barrier having a plurality of openings therein throughwhich radiation eflective to irradiate other gaps may pass.

STANLEY w.

REFERENCES CITED The following references are of record in the tile ofthis patent:

UNITED STATES PATENTS Number Name Date 1,561,249 Kraut Nov. 10, 19251,664,194 Creighton Mar. 2'7, 1928 2,151,559 McEachron Mar. 21, 19392,279,249 Roman Apr. 7, 1942

